Sergio Carracedo 
Recently, one of our clients for whom we designed and programmed an online store using Drupal 7 and Drupal commerce had several needs regarding invoicing.
First, they needed orders to automatically generate a series of invoice numbers for each year, in the format 2018-123, 2018-124, … So far so normal, one of the contributed modules of Drupal Commerce.
This module is called Commerce Billy, and it meets this need, in addition to providing PDF invoice generation, the possibility of automatic or manual invoicing, and a long list of small but useful functionalities related to invoicing.
But our client, in addition to generating a series for sales invoices, needed to generate a new series in case of a return, also with consecutive numbers, but independent of the invoicing series.
Commerce Billy did not provide this functionality, so we decided to take advantage of the hooking power provided by Drupal—that is, being able to “hook” your code into different points of the program flow, allowing you to alter or extend the functionality of the core or a module without needing to modify it—and we created a simple but useful module that performs this functionality by leveraging part of Commerce Billy’s features; for example, the series type configuration (Annual, monthly, or infinite) is extracted from the one specified in Commerce Billy, simplifying the configuration for the user.
Our module is called Commerce Billy Cancel (a very original name ;) ) and we have decided to release it so that anyone with the same need as us can solve it easily.
You can download it here